In recent years, attention has been focused on organic electronic devices such as an organic EL device and an organic solar cell. Conventionally, an ITO electrode in which indium-tin composite oxide (ITO) is film-formed on a transparent substrate such as a glass plate, a plastic film or the like via a vacuum evaporation method or a sputtering method has been mainly used as an electrode for an organic electronic device in view of performance such as conductivity and transparency thereof. However, transparent electrodes prepared via vacuum evaporation or sputtering produce inferior productivity as well as high manufacturing cost. Further, there was a problem such that lifetime and a storing property of the device are degraded via damage to an organic functional layer through leakage between electrodes of the device, caused by protrusions on an ITO electrode and adhesion of foreign matter to the ITO electrode. Specifically, when preparing a large area organic electronic device, frequency of occurrence thereof is increased, resulting in appearance of a problem
In response, proposed is a method by which a transparent electrode is formed via coating or printing employing a coating solution in which a conductive polymer typified by a π conjugated polymer is dissolved or dispersed in a suitable solvent (Patent Document 1). However, since a conductive polymer was further colored in comparison to an ITO electrode, transparency of an electrode thereof largely dropped, there appeared a problem such that lifetime and a storing property of the organic electronic device were degraded.
In response, it is known that a conductive polymer typified by a n conjugated polymer is formed on an ITO electrode as a hole injection material, or a hole transparent material (Patent Document 2). In formation of the conductive polymer, protrusions and foreign mater on the ITO are to be buried to improve surface smoothness. Further, a barrier of injection of holes is lowered by forming a conductive polymer layer on an ITO transparent electrode, leading to driving voltage drop of the organic electronic device (Patent Document 2). Depending on protrusions and foreign matter in size, a conductive polymer layer necessary for burying them becomes thicker, and it is difficult to satisfy transparency of an electrode, and lifetime and a storing property of a device at the same time.
Also known is a method of forming a layer in which a conductive polymer and a non-aqueous binder are used in combination, on an ITO electrode (Patent Document 3). In Patent Document 3, disclosed is a hole injection layer containing an intrinsically conductive polymer, a dopant and a synthetic polymer-planarizing agent in a non-aqueous system. It is described that the film thickness can be thickened while suppressing reduction in transparency. However, in the case of a coating process in which a synthetic polymer and a conductive polymer were used in a non-aqueous system, surface smoothness at the nano-level became inferior when thickening the film thickness, wherein as a result, there appeared a problem such that lifetime and a storing property of the device were degraded via rise of the driving voltage. Further, a non-aqueous solvent was conventionally used when forming an organic functional layer, but there appeared another problem such that the upper layer to be coated was damaged when using a non-aqueous binder, whereby lifetime and a storing property of the device were degraded. Furthermore, since a synthetic polymer in the non-aqueous system conventionally produced no effect to assist conductivity, there was a problem such that just to mix a small amount of it produced large drop in conductivity of the film, and as a result, the film thickness could not be thickened.